When implementing automatic door operators for opening doors such as garage doors, it is common to employ a motor which moves a door between opened and closed positions in response to control signals. Such control signals are typically generated by a portable radio frequency transmitter, and/or a wall mounted push button transmitter. Furthermore, techniques are provided for detecting door obstructions to prevent personal injury or property damage caused when the control door unintentionally closes on an object or person. Such obstruction detection prevents damage to the door as well as damage to the driving components which move the door. Furthermore, it is clear that a mechanically operated door poses a particular risk to children who are playing with the automatic garage door operator.
In one form, obstruction detection is performed by monitoring the tension of a drive chain interconnecting the motor with the door. Typically, the motor is coupled to the door with a chain or a screw drive mechanism. By mechanically linking the motor with the chain by a switch which is closed under normal conditions, but opened when the drive chain exceeds a predetermined amount, a switching effect can be provided for triggering the abortion of door operation. For example, a micro-controller is often used to detect such a switch state which aborts door operation when the switch is tripped to an open position. Typically, the micro-controller is programmed to stop the door when the switch is tripped while the door is opening, and stop the door and reverse its direction until it is fully opened when it detects an open switch while closing the door.
However, the aforementioned obstruction detectors provide only limited detection capability and are usually insufficiently sensitive to prevent all injuries. Therefore, attempts have recently been made to provide supplemental detection, as well as improve existing detection when sensing door obstruction. Furthermore, recent state regulatory authorities have proposed further stricter requirements which require additional obstruction detection. Such systems incorporate radiant obstruction detectors, generally using infrared or visible light, which is projected across a lower portion of the opening for a controlled door. By breaking or interrupting the radiant beam, an obstruction is detected and the automatic door operator can be directed to reverse or open up a door. An alternative additional obstruction detector utilizes a pressure sensitive strip disposed along a door's leading edge which is typically referred to as a safety edge switch. As the door is closed on an obstruction, pressure is detected on the safety edge switch which indicates the presence of an obstruction. However, these obstruction detectors require additional components, increase the cost of the systems, and require further additional power sources and electrical wiring, particularly when incorporating a switch on a door's leading edge.